Naturalism in Science

A frequent creationist tactic is to attack, not just evolution, but the very underpinnings of science itself. Specifically, some creationists – especially advocates of intelligent design – claim that a basic guiding principle of science known as naturalism is a product of bias and an unnecessary restriction, which if removed would allow scientists to reach conclusions to which they had previously blinded themselves.

The short answer to such claims is that this cannot be done. Naturalism is neither the product of bias nor unnecessary – it is a fundamental principle of science, not for philosophical but for sound practical reasons. If it were removed, science itself would be impossible. To explain why this is the case, some background information must first be provided.

As already stated, naturalism is one of the basic guiding principles of science. It requires that supernatural causes and agents must be ruled out as scientific explanations for natural phenomena; all proposed scientific explanations must be testable and repeatable, must be based on evidence and must obey physical laws. To put it another way, this scientist is not using naturalism:

This restriction to natural causes for natural events is what gives science its explanatory power. Scientists cannot, as scientists, explain an event by invoking divine intervention. They cannot say that thunder and lightning is caused by the anger of Zeus, or that schizophrenia is caused by demonic possession, or that angels push the planets around in their orbits, or that epidemic disease is a punishment for sin. And, of course, they also cannot say that every species on Earth was created by a separate, miraculous action of God. Such a statement would be unscientific – not necessarily false, just unscientific. If supernatural events do occur, science cannot study or explain them.

It is easy to see why creationists feel excluded by naturalism. Many of their beliefs explicitly include miracles, which are forbidden in the arena of science. As a result, creationists often respond by crying bias and making accusations of foul play. They complain that naturalism is an unjustifiable metaphysical assumption that rules out entire classes of perfectly valid explanations, a ploy by atheist scientists who assume at the outset that God does not exist and tailor their investigations accordingly.

To show why this is false, a distinction must be drawn between methodological naturalism and metaphysical naturalism. The former is what science employs: the belief that natural events have natural causes and that there are physical laws which we can discover and understand. The latter is the belief that there is nothing beyond those natural causes and physical laws, in other words, that the supernatural does not exist. This is a personal belief that some scientists hold, but that science in general does not require. Science must assume that all events it can observe and study are natural in origin, but it does not claim that the supernatural does not exist; nor does it claim that it does exist. That is simply not a topic which it can speak to, and to make a statement either way would be beyond the bounds of science.

Creationists attempt to blur the distinction between these two, but the difference is not hard to grasp. Methodological naturalism is a statement about how we study the world; metaphysical naturalism is a statement about what exists. It is not necessary to be an atheist (a metaphysical naturalist) to do science. One can believe in God and still be a methodological naturalist, and there are many scientists who are. For example, one of evolution’s best-known and most articulate defenders today is Dr. Kenneth Miller, a Christian and author of the book Finding Darwin’s God. In fact, as the creationists never tire of pointing out, many of history’s great scientists were religious. A religious scientist is absolutely free to believe that miracles do occur but are beyond scientific study, or that God usually works through natural mechanisms rather than suspending the laws of nature to accomplish his will. There is nothing about scientific naturalism that denies the existence of God, but there are real reasons why it is an absolute must for science, to which this essay will now turn.

Naturalism is an absolutely essential part of science for the clear reason that naturalism is the only thing that gives science any explanatory power at all. With naturalism in place, scientists are restricted to testable answers supported by evidence. Without naturalism, there would be no such requirement, and scientists would be quite literally free to make up absolutely any answers they want, postulating unseen supernatural beings and untestable miracles as explanations for any phenomena. How did life come into being? God did it! Why does Planck’s constant have the value it does? God made it that way! Why is the universe expanding? Because God wants it to, of course! Without naturalism, there’s no reason to study how abiogenesis might have occurred, no need to formulate a grand unified theory of physics, and no point in trying to determine the nature of dark energy, because God explains it all.

Without a need to come up with evidence-based explanations that obey physical laws, there is no reason to do research, because there is no way to truly understand anything, no way to learn. The creationists who reject naturalism’s role in science are proposing that the growth of human understanding and science itself be brought to a halt. After all, once one has concluded a supernatural event occurred, there is nothing more to do, no further conclusions to draw. Supernatural influence, by definition, is not testable, obeys no laws that we can know, and does not leave any evidence at all. If these things were not the case, it would no longer be supernatural, but natural.

Naturalism is what allows science to progress. Whenever we see some event that appears to violate physical laws, using our assumption of naturalism we can conclude that this is not actually what has happened, that our understanding of the laws is faulty or incomplete, and so we must search for a new and better set of laws that takes this phenomenon into account. If we instead conclude that a supernatural event has occurred, there is nothing more that can be done, as the supernatural by definition does not defy our understanding of the laws, but the laws themselves.

This regularity is crucial if science is to be possible. If there existed an omnipotent, undetectable God who intervened in the world at unpredictable times in unpredictable ways, it would be impossible to do science, because we could not be certain that our past experience will be a reliable guide to the future. We could never know if an experiment succeeded where it should have failed or failed where it should have succeeded because of a miraculous and undetectable nudge from God; there would be no reason to believe that the results of an experiment yesterday would have any bearing on the theory it was designed to test.

Nor would the concept of evidence be meaningful in the absence of naturalism. Without this principle, neither the absence of supporting evidence nor the presence of contradictory evidence would be strikes against a hypothesis, because this could always be explained by supernatural intervention. A researcher could propose literally any hypothesis, and explain away the absence of evidence by saying God erased it and substituted new evidence as a test of faith. (It is notable that some creationists do offer exactly this defense – usually called the Omphalos or “appearance of age” argument – which claims that the Earth was created recently with only the appearance of a longer history, complete with tree rings recording years that never happened, fossils of creatures that never actually lived, and rocks whose radioactive decay “clocks” have all been set to the same spurious age.)

Finally, it is naturalism that gives science its predictive power. As already stated, the regularity and inviolability of physical law allows us to predict future events with confidence, but it goes beyond that. A theory’s predictive power comes also from its ability to rule out many possibilities. For example, the theory of evolution predicts that we should never find a mammal with feathers, because that adaptation appeared in the bird lineage, where it cannot be transmitted horizontally across the tree of descent to mammals, and such a complex structure is unlikely to evolve in exactly the same way twice. But creationism and other non-naturalistic alternatives do not predict this, and in fact, do not predict anything at all. If mammals were found that had feathers, or six legs, or any other adaptation, creationism could accommodate this or any other scenario with equal ease. Whatever we find, that was the way God wanted it, but we can never know in advance what God will want. Unlike evolution, creationism cannot exclude any scenario – it can never tell us what we should not expect to find – and therefore it is powerless to predict the future. If science were this way, it would be useless.

When confronted with arguments such as this and accused of wanting to rob science of all its explanatory and predictive power, creationists typically claim they have been misconstrued. They usually claim that they do not want to throw out naturalism in all branches of science, but stop short before the implicit conclusion: “only in those branches where we disagree with the results”. They would be happy to allow all other fields of science to proceed as normal, as long as they are allowed to wedge their version of God into those theories that would otherwise make them uncomfortable.

However, no creationist has ever explained why non-naturalistic explanations should be restricted to those areas where they feel conventional science is inadequate. Indeed, they have never explained how to make that distinction.
How do we tell the difference between things we do not know yet, for which a naturalistic explanation will presumably be discovered in due time, and things we will never know, for which a supernatural explanation is required? This is a very important question, but they have never even attempted to answer it. Are the opponents of naturalism claiming that human knowledge has reached its apex, that we will never learn anything more than what we know right now, and so the scientists should stand back and let them spackle in the remaining gaps with God? This is obviously false; we are making new discoveries every day. Or are they claiming every other branch of science should be allowed to proceed as normal, but they want to step in and impose their supernatural explanations on evolution? But why only evolution? Surely if God intervenes there, he may have intervened in other areas as well. How do we reliably detect supernatural influence?

That the creationists have no answer to these questions shows how poorly thought-out their arguments truly are. They have carried their attempts to defeat evolution to such an extent that they would willingly undermine all of science to achieve this goal. In the end, the motivation of those who attack naturalism’s role in science turns out to be the same motivation driving all creationists: unable to bear the thought that science might not support their interpretation of their religion, they set out to force it to be so, regardless of the truth.